$ { \left[\begin{array}{rr}{-1} & {-2} \\ {-2} & {-1} \\ {1} & {0}\end{array}\right]+\left[\begin{array}{rr}{2} & {-1} \\ {3} & {-2} \\ {-1} & {1}\end{array}\right] = {?} } $
To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{-1}+{2} & {-2}+{-1} \\ {-2}+{3} & {-1}+{-2} \\ {1}+{-1} & {0}+{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{1} & {-3} \\ {1} & {-3} \\ {0} & {1}\end{array}\right]}$